Nitrate analyzers use absorption spectroscopy to measure dissolved nitrate concentrations in natural waters, such as oceans, lakes, and rivers, often for the purpose of environmental monitoring and research. Absorption spectroscopy makes use of the characteristic of dissolved constituents in water to selectively absorb light. Molecules, ions, and chemical species in solution have unique wavelength-dependent absorption properties that allow the quantification of these dissolved constituents by measuring spectral absorption of the solution. These instruments typically contain a deuterium plasma arc lamp to provide an ultraviolet (UV) radiation source. The analyzer measures the spectral UV radiation transmitted through a water sample and compares this signal with a prior baseline measurement of pure water in order to determine the absorption spectrum of the dissolved constituents (e.g., nitrate) in the sample.
Conventional broadband UV radiation sources such as deuterium and hydrogen discharge lamps suitable for measurement of radiation absorption in aqueous solutions are high power, costly, physically large, slow to stabilize, and the radiation output used for the absorption measurement can only be controlled by lamp pulse width and/or detector integration time. Consequently, instruments using such sources for measuring chemical species dissolved in water with UV absorption, (1) have limited control of radiation output which limits measurement performance in terms of accuracy, precision, sensitivity and range, and (2) require complex control, power electronics, and heat management schemes that make them too complex and expensive to be practical for the environmental monitoring market.
The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claimed embodiments. Further, the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be expanded or reduced to help improve the understanding of the embodiments. Moreover, while the disclosed technology is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to unnecessarily limit the embodiments described. On the contrary, the embodiments are intended to cover all suitable modifications, equivalents, and alternatives falling within the scope of the embodiments as defined by the appended claims.